Concluding answer in case someone has the same problem:
- made adapter pcb with level shifting 3.3V to 2.8V
- changed toradex BSP files (devicetree, config (include drivers into kernel), and drivers see below) via the instructions in the “patching the kernel” blog entry
Then proceeded to have a lot of issues (as described in the comments below jaskis answer), which stopped it from working, which were solved by:
- issue 1, which caused the start up problems of the camera was, that I misconfigured the reset pin to high active instead of low active (since low_active for some reson is 1 in the devicetree)
- other issues were solved by merging camera-module manufacturers (phytec) driver for the imx6ul into the driver in the BSP, which seems to include all the necessary workarounds (see files)
Now the whole thing can take photos! Thank you for the input @jaski.tx. Sadly I wont be continuing the project since the company has decided to let student contracts run out due to corona.